1. Field of the Invention
This invention relates to a method of preparing a dental prosthetic construction, and particularly a crown or bridge, of ceramic fired to precious metal alloys containing silver.
2. Discussion of Prior Art
Dental prosthetic constructions made of ceramic fired to metallic materials, also known as composite metal/ceramic dental reconstructions, are prepared by firing dental ceramic compositions onto appropriately configured metal structures. To this end, the ceramic compositions, which consist mainly of an opaque base composition, a color-bearing dentin composition and a transparent incisal composition, are applied in the form of usually aqueous slurries in successive layers to structures cast from alloys which either contain precious metals or are free of them, dried, and fired. The firing temperature ranges from about 900.degree. to 1000.degree. C.
Firing of the dental ceramic compositions is usually done in vacuum furnaces in whose firing chambers a reduced pressure with a residual atmospheric-oxygen content can be established.
Apart from silver-free precious-metal alloys on a gold basis, less costly alloys containing palladium, silver, and less gold than gold-based alloys, or no gold at all, are being used increasingly in the field of dentistry.
When silver-containing precious-metal alloys are used as baking alloys, the ceramic facings sometimes exhibit undesirable yellowing after firing.